postelsia 35 



prairie clovers (Petalostemon spp.) and 

 the sunflowers. With the coming on 

 of autumn the mesas are green with 

 the herbage of Senecio and Gutierrezia, 

 which, as they come into blossom, im- 

 part a yellow tinge to the entire land- 

 scape. These two dominant species of 

 the herbaceous flora of autumn have 

 arrived from different regions. The 

 Senecio (sp. undet.) occurs regularly in 

 the mountains at higher levels, while 

 Gutierrezia is properly a plant of the 

 plains, and in northern Colorado does 

 not ascend into the mountains at all. 

 The Plants of the Lower Foothills, 

 These resemble those of the mesas. 

 Similiar conditions of moisture and heat 

 prevail. For the most part the lower 

 foothills are sparingly covered with 

 pines. The north slopes of hills are 

 better provided with trees than the 

 south slopes. Spruces and cedars are 



